CN112521171B - Anisotropic permanent magnetic ferrite and preparation method thereof - Google Patents
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Abstract
The invention belongs to the technical field of permanent magnetic ferrite, and discloses an anisotropic permanent magnetic ferrite and a preparation method thereof, wherein the preparation method comprises the following steps: (1) Adding polyvinyl alcohol into water to obtain a polyvinyl alcohol dilute solution, wherein the polyvinyl alcohol accounts for 0.1-2wt% of the polyvinyl alcohol dilute solution; (2) Adding the ferrite magnetic powder into the polyvinyl alcohol dilute solution, and stirring and mixing to obtain slurry; the mass ratio of ferrite magnetic powder to polyvinyl alcohol dilute solution in the slurry is 3: (1.2-3); (3) Drying the slurry at a low temperature of 70-80 ℃, crushing after drying, adding a lubricant, stirring and dispersing to obtain anisotropic permanent magnetic ferrite powder; (4) And (3) placing the anisotropic permanent magnetic ferrite powder in a magnetic field, dry-pressing and molding, sintering and grinding to obtain the anisotropic permanent magnetic ferrite. The anisotropic permanent magnetic ferrite product prepared by the preparation method has excellent forming effect and magnetic comprehensive performance.
Description
Technical Field
The invention belongs to the technical field of permanent magnetic ferrite, and particularly relates to an anisotropic permanent magnetic ferrite and a preparation method thereof.
Background
The permanent magnetic ferrite is formed by a wet pressing method and a dry pressing method. Compared with the wet pressing method, the magnetic performance of the product prepared by the dry pressing method is lower, but the dry pressing method has the following advantages: (1) The magnet with smaller size and more complex shape is easy to form; (2) water pumping is not needed; (3) The formed blank is smooth and flat, can be blown off only by blowing with strong wind, does not need fettling, and reduces the workload. The process of dry pressing anisotropic products is still widely used. In the dry pressing process, since the ferrite magnetic powder has no tackiness, a binder (adhesive) and a lubricant are used in the process of preparing the product by the dry pressing method to ensure the mechanical strength and appearance of the blank. The camphor has the dual properties of lubrication and bonding, the lubrication is mainly performed when the camphor is not compressed, the bonding is mainly performed after the camphor is compressed, and the camphor is easy to volatilize, so that the camphor can increase the dispersibility of powder materials, and is an ideal adhesive. The natural camphor has better performance, but the natural camphor is expensive and has a low material source. When the artificial camphor is adopted, the smell emitted by the artificial camphor is not good for human bodies. Along with the improvement of the environmental protection requirement, the price of the artificial camphor is also increased all the way, so that the production cost and the environmental protection cost are greatly increased. Therefore, it is important to find and research a new binder for dry-pressing permanent magnetic ferrite molding.
Researchers in the field have made many studies on the binders used for ferrite powder, and some of the binders have been successfully used for ferrite molding, for example, in the molding of isotropic ferrite powder, polyvinyl alcohol (PVA) is used as the binder, the solubility of the PVA aqueous solution used in the process is 8-13wt%, and the isotropic powder obtained in this way is easy to mold. However, in dry pressure anisotropic molding, polyvinyl alcohol as a binder has strong viscosity and poor lubricity, and powder is easy to agglomerate and peel during drying, so that poor orientation and reduced residual magnetism Br are caused, and the product effect is not ideal. After the amount of the polyvinyl alcohol is reduced, although the problem of poor orientation is improved to a certain extent, the bonding effect of the product is obviously reduced, and the two strategies are difficult to obtain.
Therefore, it is desirable to provide a method for preparing the anisotropic permanent magnetic ferrite by using polyvinyl alcohol as a binder, and to ensure that the prepared anisotropic permanent magnetic ferrite has good forming effect and remanence performance.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art described above. Therefore, the invention provides the anisotropic permanent magnetic ferrite and the preparation method thereof, and the anisotropic permanent magnetic ferrite product prepared by the preparation method has excellent molding effect and magnetic comprehensive performance.
A preparation method of the anisotropic permanent magnetic ferrite comprises the following steps:
(1) Adding polyvinyl alcohol into water to obtain a polyvinyl alcohol dilute solution, wherein the polyvinyl alcohol accounts for 0.1-2wt% of the polyvinyl alcohol dilute solution;
(2) Adding ferrite magnetic powder into the polyvinyl alcohol dilute solution obtained in the step (1), and stirring and mixing to obtain slurry; the mass usage ratio of the ferrite magnetic powder to the polyvinyl alcohol dilute solution in the slurry is 3: (1.2-3);
(3) Drying the slurry obtained in the step (2) at a low temperature of 70-80 ℃, crushing after drying, adding a lubricant, stirring and dispersing to obtain anisotropic permanent magnetic ferrite powder;
(4) And (4) placing the anisotropic permanent magnetic ferrite powder obtained in the step (3) in a magnetic field, dry-pressing and molding, sintering and grinding to obtain the anisotropic permanent magnetic ferrite.
The invention finds that the forming yield is low if the binder polyvinyl alcohol is not prepared into a solution form, but the dried polyvinyl alcohol is directly added into the magnetic powder for loosening. The invention configures the polyvinyl alcohol into the form of aqueous solution, and simultaneously, the ferrite magnetic powder and the polyvinyl alcohol dilute solution can be fully mixed, so the dosage ratio between the two is not suitable to be too small or too large.
Moreover, although the problem of poor ferrite orientation can be improved to a certain extent by using a low-concentration polyvinyl alcohol dilute solution, the bonding effect of the product is reduced obviously. The key point for overcoming the technical problem lies in that a unique low-temperature drying method is adopted, and compared with the traditional process in which high-temperature drying at more than 100 ℃ or even more than 120 ℃ is adopted to accelerate the production efficiency, the invention discovers that the combination effect of polyvinyl alcohol and magnetic powder is better through a low-temperature drying mode, the penetration of the polyvinyl alcohol between the magnetic powder is facilitated, the coating effect on the surface of the magnetic powder is improved, the coating is tighter, the thickness of the formed polyvinyl alcohol coating film is very thin (the thickness of the coating film is nano-scale and has very strong adsorbability), and the formed polyvinyl alcohol coating film can have very good viscosity after being subjected to dry pressing. The preparation method can ensure the molding effect of the special-shaped permanent magnetic ferrite product under the condition of not increasing the dosage of polyvinyl alcohol, and the prepared special-shaped permanent magnetic ferrite product has excellent magnetic comprehensive performance.
Preferably, the ferrite magnetic powder in the step (2) has a particle size of 0.65 to 0.85 μm.
More preferably, the ferrite magnetic powder in step (2) may further comprise a magnetic property enhancer selected from CaCO 3 、Al 2 O 3 、H 3 BO 3 Or SiO 2 At least one of (a).
Preferably, the lubricant in step (3) is a stearate. More preferably, the lubricant is calcium stearate.
Preferably, the lubricant is added in the step (3) in an amount of 0.2 to 1% by weight based on the weight of the ferrite magnetic powder.
Preferably, the magnetic field strength of the magnetic field in step (4) is not less than 6000Oe.
Preferably, the pressure of the dry pressing in the step (4) is 5-10MPa.
Preferably, the sintering temperature in the step (4) is 1100-1300 ℃, and the sintering time is 0.1-2h.
An anisotropic permanent magnetic ferrite prepared by the preparation method.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, the adhesive polyvinyl alcohol is prepared into a low-concentration aqueous solution, and the prepared anisotropic permanent magnetic ferrite product has good forming effect and magnetic comprehensive performance through a low-temperature drying process.
Detailed Description
In order to make the technical solutions of the present invention more clearly apparent to those skilled in the art, the following examples are given for illustration. It should be noted that the following examples are not intended to limit the scope of the claimed invention.
The starting materials, reagents or apparatuses used in the following examples are, unless otherwise specified, either commercially available from conventional sources or can be obtained by known methods.
Example 1
The embodiment provides an anisotropic permanent magnetic ferrite, and the preparation method comprises the following steps:
(1) Adding 0.6 part by weight of polyvinyl alcohol into 135 parts by weight of water to obtain a polyvinyl alcohol dilute solution, wherein the polyvinyl alcohol accounts for 0.44wt% of the polyvinyl alcohol dilute solution;
(2) Adding 300 parts by weight of ferrite magnetic powder (the particle size is 0.65-0.85 mu m) into the polyvinyl alcohol dilute solution obtained in the step (1), and stirring and mixing the mixture by using a mixing roll to obtain slurry;
(3) Drying the slurry obtained in the step (2) at a low temperature of 75 ℃, crushing the dried slurry by using a dispersion machine, adding 0.9 part by weight of lubricant calcium stearate, stirring the mixture to disperse the mixture for 3 times to obtain anisotropic permanent magnetic ferrite powder;
(4) And (4) putting the anisotropic permanent magnetic ferrite powder in the step (3) in a magnetic field of 6000Oe, performing dry pressing molding under the pressure of 5MPa, sintering the blank at 1210 ℃ for 1h, and grinding to obtain the anisotropic permanent magnetic ferrite.
Example 2
The embodiment provides an anisotropic permanent magnetic ferrite, and the preparation method comprises the following steps:
(1) Adding 0.6 part by weight of polyvinyl alcohol into 255 parts by weight of water to obtain a polyvinyl alcohol dilute solution, namely the polyvinyl alcohol accounts for 0.23wt% of the polyvinyl alcohol dilute solution;
(2) Adding 300 parts by weight of ferrite magnetic powder (the particle size is 0.65-0.85 mu m) into the polyvinyl alcohol dilute solution obtained in the step (1), and stirring and mixing the mixture by using a mixing roll to obtain slurry;
(3) Drying the slurry obtained in the step (2) at a low temperature of 80 ℃, crushing the dried slurry by using a dispersion machine, adding 0.9 part by weight of lubricant calcium stearate, stirring the mixture to disperse the mixture for 3 times to obtain anisotropic permanent magnetic ferrite powder;
(4) And (4) placing the anisotropic permanent magnetic ferrite powder in the step (3) in a 7000Oe magnetic field, carrying out dry pressing molding under the pressure of 8MPa, sintering the blank at 1210 ℃ for 1h, and grinding to obtain the anisotropic permanent magnetic ferrite.
Comparative example 1
The comparative example provides an anisotropic permanent magnetic ferrite using camphor as a binder, and the preparation method thereof comprises the following steps:
(1) Weighing 300 parts by weight of a magnetic powder raw material which is the same as the ferrite magnetic powder used in example 1, then adding 2.4 parts by weight of camphor and 0.9 part by weight of calcium stearate, and stirring to obtain a mixture;
(2) And (2) scattering the mixture obtained in the step (1) by using a high-speed dispersion machine, placing the mixture in a 7000Oe magnetic field for compression molding (the compression pressure is 10 MPa), sintering the blank at 1210 ℃ for 1 hour, and grinding to obtain the anisotropic permanent magnetic ferrite.
The comparative example is high in cost and not environmentally friendly since camphor is used as a binder.
Comparative example 2
The comparative example provides an anisotropic permanent magnetic ferrite, and the preparation method comprises the following steps:
(1) Adding 0.6 part by weight of polyvinyl alcohol into 6 parts by weight of water to obtain a polyvinyl alcohol dilute solution, wherein the polyvinyl alcohol accounts for 9.1wt% of the polyvinyl alcohol dilute solution;
(2) Adding 300 parts by weight of ferrite magnetic powder (the particle size is 0.65-0.85 mu m) into the polyvinyl alcohol dilute solution obtained in the step (1), and stirring and mixing the mixture by using a mixing roll to obtain slurry;
(3) Sieving the slurry obtained in the step (2) by a 40-mesh sieve, taking out the slurry, drying at a low temperature of 75 ℃, crushing by a dispersion machine after drying, adding 0.9 part by weight of lubricant calcium stearate, stirring for dispersing, and dispersing for 3 times to obtain anisotropic permanent magnetic ferrite powder;
(4) And (4) placing the anisotropic permanent magnetic ferrite powder in the step (3) in a 7000Oe magnetic field, carrying out dry pressing molding under the pressure of 7MPa, sintering the blank at 1210 ℃ for 1h, and grinding to obtain the anisotropic permanent magnetic ferrite.
The magnetic powder prepared by the process of the comparative example can not be molded and is broken when a blank body is pressed, so that no subsequent performance test data exists.
Comparative example 3
The comparative example provides an anisotropic permanent magnetic ferrite, and the preparation method comprises the following steps:
(1) Adding 3 parts by weight of polyvinyl alcohol into 30 parts by weight of water to obtain a polyvinyl alcohol dilute solution, wherein the polyvinyl alcohol accounts for 9.1wt% of the polyvinyl alcohol dilute solution;
(2) Adding 300 parts by weight of ferrite magnetic powder (the particle size is 0.65-0.85 mu m) into the polyvinyl alcohol dilute solution obtained in the step (1), and stirring and mixing the mixture by using a mixing roll to obtain slurry;
(3) Sieving the slurry obtained in the step (2) by a 40-mesh sieve, taking out the slurry, drying at a low temperature of 75 ℃, crushing by a dispersion machine after drying, adding 0.9 part by weight of lubricant calcium stearate, stirring for dispersing, and dispersing for 3 times to obtain anisotropic permanent magnetic ferrite powder;
(4) And (4) placing the anisotropic permanent magnetic ferrite powder in the step (3) in a 7000Oe magnetic field, carrying out dry pressing molding under the pressure of 8MPa, sintering the blank at 1210 ℃ for 1h, and grinding to obtain the anisotropic permanent magnetic ferrite.
Comparative example 4
The comparative example differs from example 1 only in that: and (4) drying at 150 ℃ in the step (3), wherein the rest preparation method is completely the same as that in the example 1.
Product effectiveness testing
The magnetic properties of the anisotropic permanent magnetic ferrites prepared in examples 1-2, comparative example 1, comparative example 3 and comparative example 4 (the magnetic properties of the product prepared in comparative example 2 were not determined because the product could not be molded) were measured by using an AMT-4 permanent magnet automatic measuring instrument, and the test results are shown in Table 1; the average strength of the anisotropic permanent magnetic ferrite was measured again, and the measurement results are shown in table 2.
TABLE 1 magnetic Properties of Anisotropic permanent magnetic ferrites
| Test article | Br(mT) | Hcb(kA/m) | Hcj(kA/m) | (BH) max (kJ/m 3 )) |
| Example 1 | 0.378 | 245.9 | 258.0 | 27.89 |
| Example 2 | 0.377 | 246.8 | 259.1 | 27.46 |
| Comparative example 1 | 0.375 | 234.7 | 245.3 | 27.07 |
| Comparative example 3 | 0.309 | 219 | 274 | 17.9 |
| Comparative example 4 | 0.377 | 234 | 246 | 27.6 |
TABLE 2 average Strength of Anisotropic permanent magnetic ferrites
As can be seen from Table 1, the magnetic properties of the anisotropic permanent magnetic ferrites obtained in examples 1-2 were not significantly changed as compared with comparative example 1 using camphor as a binder, confirming that the preparation process of the present invention can overcome the defect of the decrease in magnetic properties when polyvinyl alcohol was used as a binder. From comparative example 3, it can be seen that the concentration of the polyvinyl alcohol solution and the mass ratio thereof to the ferrite magnetic powder have an influence on the magnetic properties of the product, and the magnetic properties of the product are seriously degraded. As can be seen from comparative example 4, an excessively high baking temperature may deteriorate the magnetic properties of the product to some extent.
As can be seen from table 2, although the average strength of the anisotropic permanent magnetic ferrite products in examples 1-2 is somewhat decreased compared to comparative example 1, the decreased molding effect can already satisfy the actual requirement without excessively high average strength. In contrast, the average strength value of the anisotropic permanent magnetic ferrite product in the comparative example 3 is reduced to only 321.55N, and the phenomena of powder falling, peeling or cracking begin to appear, so that the actual product requirements cannot be met. While the average strength value of the anisotropic permanent magnetic ferrite product in the comparative example 4 is reduced to 205.54N, the strength performance is seriously lost, which indicates that when the usage amount of the polyvinyl alcohol is less, the excessive drying temperature can seriously affect the bonding performance of the polyvinyl alcohol, and the strength of the product is obviously reduced.
Claims (8)
1. The preparation method of the anisotropic permanent magnetic ferrite is characterized by comprising the following steps of:
(1) Adding polyvinyl alcohol into water to obtain a polyvinyl alcohol dilute solution, wherein the polyvinyl alcohol accounts for 0.1-0.44wt% of the polyvinyl alcohol dilute solution;
(2) Adding ferrite magnetic powder into the polyvinyl alcohol dilute solution obtained in the step (1), and stirring and mixing to obtain slurry; the mass ratio of ferrite magnetic powder to polyvinyl alcohol dilute solution in the slurry is 3: (1.2-3);
(3) Drying the slurry obtained in the step (2) at a low temperature of 70-80 ℃, crushing after drying, adding a lubricant, stirring and dispersing to obtain anisotropic permanent magnetic ferrite powder;
(4) And (4) placing the anisotropic permanent magnetic ferrite powder obtained in the step (3) in a magnetic field, dry-pressing and molding, sintering and grinding to obtain the anisotropic permanent magnetic ferrite.
2. The production method according to claim 1, wherein the ferrite magnetic powder in the step (2) has a particle size of 0.65 to 0.85 μm.
3. The production method according to claim 1, wherein the lubricant in step (3) is a stearate.
4. The production method according to claim 1, wherein the lubricant is added in an amount of 0.2 to 1% by weight of the ferrite magnetic powder in step (3).
5. The method according to claim 1, wherein the magnetic field strength of the magnetic field in the step (4) is not less than 6000Oe.
6. The production method according to claim 1, wherein the pressure for the dry-pressing in the step (4) is 5 to 10MPa.
7. The method according to claim 1, wherein the sintering temperature in the step (4) is 1100 to 1300 ℃ and the sintering time is 0.1 to 2 hours.
8. An anisotropic permanent magnetic ferrite produced by the production method according to any one of claims 1 to 7.
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| KR100615043B1 (en) * | 2004-08-27 | 2006-08-25 | 강규채 | Method for preparing the magnet using said ferrite powder and strontium powder |
| JP2006143530A (en) * | 2004-11-19 | 2006-06-08 | Sumida Corporation | Ni-Zn BASED FERRITE COMPOSITION AND MAGNETIC ELEMENT |
| CN101205137A (en) * | 2007-01-18 | 2008-06-25 | 横店集团东磁股份有限公司 | Method for manufacturing dry-pressing formed sintered permanent ferrite |
| CN101276668A (en) * | 2008-02-02 | 2008-10-01 | 河北工业大学 | Method for preparing nano soft magnetic manganese-zinc ferrite |
| DE102013213494A1 (en) * | 2013-07-10 | 2015-01-29 | Volkswagen Aktiengesellschaft | Method for producing a permanent magnet and permanent magnet and electric machine with such a permanent magnet |
| CN104496458A (en) * | 2014-09-22 | 2015-04-08 | 横店集团东磁股份有限公司 | Manufacturing method of dry-pressed anisotropic ferrite magnetic powder |
| CN104446411A (en) * | 2014-11-13 | 2015-03-25 | 常熟市三佳磁业有限公司 | Preparation method of manganese-zinc ferrite particles |
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